In the beginning of the Mexican-American War, United States Army Lt. Colonel Stephen W. Kearny brought 1,700 soldiers from Leavenworth, Kansas, through the contested Indian territory, to secure the New Mexico territory for the United States. Manuel Armijo, Provincial Governor of the New Mexican territory, learned of the invasion in June of 1846 from an American business partner, who arrived with a caravan from Independence, Missouri. On August 8th, Armijo issued a proclamation to the people of New Mexico, exhorting them to prepare to repel the American invasion.

On August 9th, Armijo called a meeting with a number of New Mexican leaders. He did not want to fight, but the parish priests, the regular-army commander, Diego Archuleta, and the militia officers Manuel Chaves and Miguel Pino wanted to defend their land.

According to some accounts, Armijo would have done nothing toward defense if Chaves and Pino hadn't forced him. On Aug 12th he received an American named James Magoffin who later claimed to have convinced Armijo and Archuleta not to fight. Soon, some Mexicans, frustrated at the thought of an American invasion, and the possible subsequent loss of their lands, talked of killing the American traders in town, but Armijo convinced them otherwise.

In preparing for the defense of Santa Fe, Armijo set up a position east of the pueblo in a narrow pass, but eventually decided not to fight. When Pino, Chaves, and the militia insisted, Armijo ordered the cannon pointed at them. On August 14th, Upon confirming the size of the American force that would soon be arriving, most of the Mexican forces decided to returned to their homes in Santa Fe, while Armijo and some of the regular Mexican soldiers rode south to Chihuahua.

Kearny and his troops encountered no Mexican forces when they arrived on August 15. Kearny and his force entered Santa Fe and claimed the New Mexico Territory for the United States without a shot being fired. From Santa Fe, Kearny sent Colonel Alexander Doniphan further south into Mexico. Kearny declared himself the military governor of the New Mexico Territory on August 18 and established a civilian government. He then took the remainder of his army west to Alta California. The New Mexicans put up no organized resistance until the Taos Revolt in early 1847.